Adjustable cam structure



0a. 11, 1949. B. A. EELS 2,484,331

ADJUSTABLE cm STRUCTURE Filed Dec. 6/1945 2 Sheets-Sheet 1 OSCILLATION GENERATOR INVENTOR. BASIL' A. BELS Oct. 11, 1949. B. A. BELS ADJUSTABLE cm swnucruma 2 Sheets-Sheet 2 Filed Dec. 6, i94

' INVENTOR. BASIL A. BELS ATTJ NEI FIG .3

Patented Oct. 11, 1949 ADJUSTABLE CAM STRUCTURE Basil A. Beis, Great Neck, N. Y., assignor, by mesne assignments, to Hazeltine Research, Inc., Chicago, 111., a corporation of Illinois Application December 6, 1945, Serial No. 633,206

7 Claims.

1 This invention is directed to a control mechanism. While being subject to a variety of applications, the invention is especially suited for con- .trolling the variable element of an adjustably tuned circuit and will be particularly described in that connection.

As is well known, adjustably tuned circuits are widely employed in communication, electronic and similar apparatus. Where the apparatus is to operate over a range of frequencies or wave lengths, a control arrangement is customarily provided for controlling the variable elements of the tuned circuits to facilitate tuning to any selected point within the range. The nature of the control mechanism is dictated to some extent by the physical structure of the tuned circuit. Often times the control mechanism features a longitudinally displaceable member or plunger, mechanically coupled with the adjustable element of the tuned circuit to control the circuit in accordance with the position of the tuning plunger. Such an arrangement is desirable because of its simplicity of operation and construction.

In order to effect longitudinal displacements of the tuning plunger in control mechanisms of the type mentioned above, it has been proposed to provide a. rotatable cam positioned so that the plunger may engage it as a cam follower. By suitably shaping the cam contour, the plunger may be selectively displaced upon rotation of the cam to adjust the tuned circuit, as desired, over a range of operating frequencies. In this prior mechanism the rotary motion of the cam is translated to linear motion of the tuning plunger.

-While it may accomplish the desired tuning adjustment, it is especially sensitive to the play of the cam with respect to its shaft which has a marked effect on the accuracy of tuning. For this reason, such arrangements may be undesirable in certain installations.

Another prior control mechanism comprises a rotatable disc including a circular series of individually adjustable stop pins, projecting from the plane of rotation of the disc to engage one end of a longitudinally adjustable tuning plunger. The pins are spaced close together effectively to constitute a continuous cam track and the end of the plunger is formed into a cam surface for following the cam track upon rotation of the disc. Such arrangements have a definite limitation as to the permissible differential height of succeeding pins. Adjacent pins must be of sufllcient relative heights to enable the plunger to engage each one and to permit rotating the disc so that the plunger may be advanced from pin to pinto 2 tune the circuit in accordance with the preselected heights of the pins. Such limitations may render this type of control arrangement undesirable.

It is an object of the present invention, therefore, to provide a control mechanism which substantially avoids one or more of the above-mentioned limitations of prior arrangements.

V It is another object of the invention to provide an improved control mechanism of simplified and inexpensive mechanical construction.

It is a further object of the invention to provide an improved control mechanism for adjusting a control element and including provisions for accurately efiecting preselected adjustments of the controlled element.

A control mechanism in accordance with the invention comprises a first longitudinally extending member including a predetermined portion and a second longitudinally extending member including a circular portion having a first sector with a leading edge and a trailing edge and having a second sector. The mechanism also includes means for supporting the aforesaid members for unidirectional rotational displacement and for bidirectional longitudinal displacement relative to one another and for positioning said members so that the circular portion of the second member defines the locus of points thereof in longitudinal alignment with a predetermined portion of the first member. The members are biased toward a reference position, representing a minimum longitudinal separation therebetween, and are adapted to control a controlled element in accordance with the displacements of said members from the reference position. A preset cam projects longitudinally from the first sector of the second member and comprises an inclined surface which extends from the leading edge to the trailing edge of the first sector, the slope of the aforesaid surface being proportioned to displace the first member longitudinally from its reference position to a preset position, corresponding to a maximum separation of the members. Also, a plurality of individually adjustable stop devices project longitudinally from and are spaced along the second sector of the second member, the projection of the stop devices being in a descending progression from the trailing edge of the first sector so that upon relative rotation of the members the stop devices successively engage the first member to eflect preselected and progressively increasing longitudinal displacements of the first member from its preset position toward the reference position.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying arrangement there represented includes an oscil-- lation generator i9 and a control mechanism ll, embodying the present invention and associated with an adjustably tuned circuit of the generator for selectively adjusting the operating wave length thereof to any one of a number of preselected values. The generator may have any conventional design and construction but it will be assumed to operate at ultra-short wave lengths. It is represented in block diagram, a portion of which is broken away to reveal an adjustably tuned circuit. As illustrated, this circuit is of the reentrant type and comprises a short-circuited transmission-line section. The transmission-line section is provided by an inner conductor l2 and a coaxially aligned outer conductor i3 which are short-circuited at one end as indicated at M. A tuning plunger I5 is electrically and mechanically connected at the opposite end of outer conductor I3, being positioned to project within inner conductor l2. The plunger l5 effectively continues the outer conductor l3 and may be considered as a re-entrant extension thereof which is adjustable in order to vary the eifective electrical length of the transmission line of the generator. A similar re-entrant tunable circuit is disclosed in Fig. 5 of United States Letters Patent 2,085,223 to F. A. Kolster, issued June 29, 1937.

The control mechanism I l includes a housing 29 i and a removable cover plate 2|, having a centrally located aperture 22. First and second longitudinally extending members, defined more particularly hereinafter, are supported by this housing for both'rotational and longitudinal displacement relative to one another. These members are normally biased together toward a reference position, representing a minimum longitudinal separation of the members, and are adapted to control a controlled element in accordance with their displacement from the reference position of minimum longitudinal separation. The first member is a plunger 23 and the second is a cylinder 24. These members are. in space-opposed relation, being positioned at opposite ends of housing 20.

The plunger 23 is supported for longitudinal displacement, slidably projecting through aperture 22 of the cover plate 2l. A coil spring 25, anchored at one end to cover plate 2| and at the other to a collar 26 secured to the plunger, serves to bias the plunger in the direction of cylinder 24. The end of the plunger enclosed within housing 20 has a right-angle bent portion 21 to which is secured a bracket 29. The bracket supports a rotatable cam follower or roller 29 and a. stop abutment in side-by-side relation. The opposite end of plunger 22 which projects beyond housing 29 is mechanically coupled to tuning plunger l5 of oscillation generator. I0, as indicated by broken construction line 2|.

The cylinder 24 is rotatably supported n a coaxial shaft which is accommodated by a bearing 36 formed in housing 20. The location of bearing 36 with reference to the aperture 22 and the diameter of cylinder 24 are selected so that a circular peripheral portion of the cylinder defines the locus of points longitudinally aligned with a predetermined portion, specifically the end portion, of plunger 23 including cam follower 29 and stop abutment 30. In other words, the selection is such that the cam follower 29 and the stop abutment 30 are in longitudinal alignment with cylinder 24 so that rotation of the cylinder about its own axis defines a circular area including all points aligned with elements 29 and 30 for any position of the cylinder. A collar 31 is secured near one end of shaft 35 to'rest against one end of bearing 36 and maintain a desired position of the shaft within the housing 20. 1

Relative rotation of plunger 23 and cylinder 24 required to efiect controlled longitudinal displacement of the plunger, in a manner to be made clear hereinafter, is accomplished by a driving motor 40 which is rotated in a single direction. A

coupling 4| mechanically connects the shaft 42 of the motor to a stub shaft 43 rotatable within a bearing 44 formed ina side wall of housing 20. The free end of shaft 43 carries a beveled gear 45 which is in meshing engagement with a similar beveled gear 46, freely rotatable upon a fixed threaded shaft 41 also supported by housing 20. An additional gear 48 rotates with beveled gear 46 and is in meshing engagement with a gear 49 formed on the external periphery of cylinder 24 for driving the cylinder in a given direction.

A preset cam 50 projects from one sector of the above-defined circular portion of cylinder 24 and is proportioned to engage cam follower 29 upon relative rotation of members 23 and 24 in a given direction to displace these members longitudinally from their reference position of minimum longitudinal separation to a preset position, corresponding to a maximum longitudinal separation. A plurality of individually adjustable stop devices or pins 5|, 5| project from and are spaced along another sector of the aforementioned circular portion of cylinder 24 with the leading stop device adjacent the trailing edge of cam 50. The separation of the pins is such that upon relative rotation of members 23 and 24 in a counterclockwise direction the stop devices 5| successively engage stop abutment 30 to eifect preselected and progressively increasing longitudinal displacements of the members 23 and 24 from their preset position toward their reference position.

The relative positions of preset cam 50 and the adjustable stop pins 5! are clearly shown in Figs. 2 and 3 which are a plane view and a sectional view, respectively, of the assembly including cylinder 24. The cylinder is rotated in a counterclockwise direction and the trailing edge of cam 50 is designated 50a. The leading stop pin is designated 5la. It is closely spaced with reference to cam edge 50a so that upon rotation of cylinder 24 stop abutment 30 of plunger 23 is engaged by stop pin 5|a just as cam follower 29 leaves the trailing edge of cam 50. The spacing of the stop pins 5|, 5| with reference to one another is such that the stop abutment 30 may travel from one pin to the next upon rotation of cylinder 24 without falling between any pair of pins which would arrest cylinder rotation. The number of stop pins provided corresponds to the number of preset tuning adjustments desired for generator l9. As illustrated, twelve stop pins are included within cylinder 24, enabling twelve discrete tuning adjustments oi the gen orator.

Referring now to Fig. 3, each stop pin Ii oomprises a rod s'ection lib which carries an internally thre'aded sleeve lie at one end. Therod section lib extends through an aligning cylinder III which is constructed to have tiers or sections of diilerent longitudinal thickness. The aligning cylinder 80, as indicated in Fig. 2, has a lower tier Si or a section of minimum longitudinal thickness, a middle tier 2 and a top tier II. The purpose of the tier construction is to permit sub stantially the same portion or the rod section ill) of any pin to project above the aligning cylnecessary that the pins, when viewed in the direction of cylinder rotation, project decreasing amounts above the cylinder 24 but the projection a or any pin will be in accordance with a desired inder Bil. This adds mechanical strength to the pin arrangement. Each internally threadedportion bio of the pins is shouldered to engage the aligning cylinder 80 and limit its vertical travel.

Additionally, each sleeve portion Iic has a projection 5id which is received by an aligned slot in a spider 65 coaxially positioned within operating condition of the oscillation generator. The projection of the leading'pin 5ia must be no greater than the projection of the trailing edge Illa oi the preset cam. Let it further be cylinder 24. The engagement of projection 5id with a slot of spider 65 permits longitudinal but prevents rotational displacement of any pin 5i. Longitudinal adjustment of any pin is accomplished by an externally threaded screw 88 which engages the internally threaded sleeve iiic of the particular pin. Each screw 66 has a tapered portion. which is received by a complementary tapered aperture in the end wall of cylinder 24. The free end of each screw is formed into a key 58 through which the screw may be rotated to adjust its pin iii to a preselected height. A spring spider 69 engages each screw 66 to retain the screw properly situated within cylinder 24. A machine screw Iii holds the spring spider in position, while machine screw lilocks the aligning cylinder 60, spider 65 and cylinder 24 into one assembly. Near the uppermost portion of aligning cylinder Bil there is positioned a bearing 12 for cylinder shaft 35.

The control circuit of Fig. 4 constitutes means for selectively controlling the driving motor 40 to arrest the rotation of cylinder 24 so that a preselected one of its stop pins 5i is in engagement with stop abutment 38 of plunger 23. The control circuit includes a brush l5 rotated by motor 40 as indicated by dash-dot line 16. ,The brush wipes against the plurality of terminals T1T12, one terminal corresponding with each oi the stop pins 5i located within cylinder 24. The brush may also contact a conductive segment 11, corresponding to the operating intervals in which the cam follower 29 is in engagement with cam 50 of cylinder 24.

A control switch 80, having corresponding terminals.T'1T'i2, is associated with the terminals engaged by brush 15 with corresponding terminals of each directly connected.to one another. The leads indicating such connections are broken, in part, to indicate that control switch 80 may be remote from the motor location. Switch ,88 may comprise a conductive wafer proportioned to contact brushes 8i associated with each of the terminals Ti-T'n. The wafer has a recessed portion 82 which is slightly less in length than the spacing between successive brushes 8!, 8|. A control knob 83 permits the recess 82 to be positioned adjacent the brush of any of terminals T'i-Tn. The wafer 80 is, grounded as is the conductive segment 11 of the switch element located at the motor installation. The brush i5 is connected through a single-pole, single-throw assumed that the switch 84 is open, motor 43 is de-energized, and the position of cylinder 24 is segment 11, asrepresented in the broken-line construction of Fig. 4.

It, now, remote control switch 88 is positioned as illustrated in Fig. 4 and switch 84 is closed, the motor is energized through conductive segment ll, brush i5, switch 84 and battery 85. The energization of the motor causes cam cylinder 24 to be rotated in a counterclockwise direction. During the initial rotation of cylinder 24, cam follower 23 rides along cam 50 and displaces plunger 23 longitudinally from its reference position to a preset position, corresponding to a maximum longitudinal separation of the plunger 23 with reference to cylinder 24. In the continued rotation of the cylinder, brush [5 successively engages terminals T1, T2, etc., to maintain the motor energized and continue the cylinder rotation. During this continued rotation, stop abutment 30 is successively engaged by stop pins 5i which permit plunger 23 to advance progressively increasing amounts under the influence of spring 25, advancing from the preset position in the direction of the reference position. When brush 15 engages terminal Ts, the motor circuit is interrupted at the corresponding terminal T's of the remote control switch since the discontinuity of water is adjacent this terminal. The motor stops and, as arrested, the stop pin corresponding to terminals Ts and T's is in engagement with stop abutment 30 of plunger 23. In this condition, the displacement of plunger 23 with reference to cylinder 24 is determined by the selected stop pin 5|. The plunger causes tuning element i5 of the oscillation generator to have a desired adjustment corresponding to apreselected operating wave length. a

By resetting the remote control switch 80 .to a different one of its terminals, the above-recited cycle of operation iollows, rotating cam cylinder 24 until the newly selected pin Si is in engagement with stop abutment 30 of plunger 23. At the instant these elements become engaged, the

rotation of cylinder 24 is arrested and a new opcrating condition of the oscillation generator is established. 1

In the drawings, the throw of preset cam 50 is represented as much greater than the permissible adjustment of tuning plunger I! of oscillation generator ID. This representation has been resorted to in order to have the drawings of a convenient size. It will be understood that the throw of the preset cam corresponds to a desired range of adjustments of the tuning element ii of the generator. For the simplest construction, the coupling between plunger 23 and tuning plunger I5 is a direct mechanical link and each receives the same displacement in response to rotation of cylinder 24.

It will be apparent from the foregoing discussion that cylinder 24 may adjust plungers l5 and' 23 over a given range. Occasionally, the entire range must be shifted to accommodate a new or changed operating condition of the generator. For example, if the displacement of tuning plunger l5 varies the operating wave length over a given range, it may be desired to shift the entire range to a higher or lower point. This may be accomplished by securing one of the members, such as cylinder 24, in an adjustably fixed position along a longitudinal axis. To this end, cylinder 24 has a depending collar 90 which rides against an abutment 9|, projecting into housing 20 and carried at one end of a threaded screw 92. Screw 92 has a threaded engagement with a portion 93 of a lock spring 94 secured to housing 20, through a machine screw 95.. By adjusting screw 92, abutment 9| may be elevated to-displace cylinder 24 longitudinally of its supporting shaft 35. This permits controlling the range of adjustment of oscillation generator III by the control mechanism.

The described arrangement permits closely controlled adjustments of the oscillation generator. The screw portion 66 associated with any stop pin 5| preferably has a fine thread, enabling micrometric adjustment of the stop pins.

The arrangement is simplified in that rotation in a single direction is utilized in setting the oper-,' ating wave length of the generator to any one of a number of preset conditions. Additionally, any play such as may result from the projection of plunger 23 through aperture 22 of the housing cover 2| has very little, if any, efiect in the accuracy of the tuning adjustment. Likewise, the pins 5| are assembled in a manner which minimizes the effect of play on the tuning accuracy.

' While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A control mechanism comprising: a first longitudinally extending member including a predetermined portion; a second longitudinally extendingmember including a circular portion having a first sector with a leading edge and a trailing edge and having a second sector; means for supporting said members for unidirectional rotational displacement and for bidirectional longitudinal displacement relative to one another and for positioning said members so that said circular portion of said second member defines the locus of points thereof in longitudinal alignment with said predetermined portion of said first member; said members being biased toward a reference position representing a minimum longitudinal separation therebetween and' being adapted to control a controlled element in accordance with the displacements of said members from said reference position; a preset cam projecting longitudinally from said first sector and comprising an inclined surface which extends irom said leading edge to said trailing edge of said first sector, the slope of said surface being proportioned to displace said first member longitudinally from said reference position to a preset position corresponding to a maximum separation of said members; and a plurality of individually adjustable stop devices projecting longitudinally from and spaced along said second sector, the projection of said. stop devices being in a descending progression from said trailing edge of said first sector so that upon relative rotation ofsaid members said stop devices successively engage said first member to effect preselected and progressively increasing longitudinal displacements of said first member from said preset .position toward said reference position; and means for effecting said unidirectional rotational displacement of said members.

2. A control mechanism comprising: a first longitudinally extending member including an end portion; a second longitudinally extending member including a circular portion having a first sector with a leading edge and a trailing edge and having a second sector; means for supporting said members in spaced opposed relation for unidirectional rotational displacement and for bidirectional longitudinal displacement relative to one another and for positioning said members so that said circular portion of said second member defines the locus of points thereof in longitudinal alignment with said end portion of said first member; said members being biased toward a reference position representing a minimum longitudinal separation therebetween and being adapted to control a controlled element in accordance with the displacements of said members from said reference position; a preset cam projecting longitudinally from said first sector and comprising an inclined surface which extends from said leading edge to said trailing edge of said first sector, the slope of said surface being proportioned to displace said first member longitudinally from said reference position to a preset position corresponding to a maximum separation of said members; and a plurality of individually adjustable stop devices projecting longitudinally from and spaced along said second sector, the projection of said stop devices being in a descending progression from said trailing edge of said first sector so that upon relative rotation of said members said stop devices successively engage said end portion of said first member to eflect preselected and progressively increasing longitudinal displacements of said first member from said preset position toward said reference position; and means for effecting said unidirectional rotational displacement of said members.

3. A control mechanism comprising: a first longitudinally extending member including a predetermined portion; a second longitudinally extending member including a circular portion having a first sector with a leading edge and a trailing edge and having a second sector; means for supporting said members for unidirectional rotational displacement and for bidirectional longitudinal displacement relative to one another and for pcfirst sector and comprising an inclined surface for engaging said cam follower, said surface extending from said leading edge to said trailing edge of said first sector and having a slope proportioned to displace said first member longitudinally from said reference position to a preset position corresponding to a maximum separation of said members; and a plurality of individually adjustable stop devices projecting longitudinally from and spaced along said second sector for 7 consecutive engagement with said stop abutment,

the projection of said stop devices being in a descending progression from said trailing edge of said first sector so that upon relative rotation of said members said stop devices successively,

engage said stop abutment to effect preselected and progressively increasing longitudinal displacements of said first member from said preset position toward said reference position; and means for effecting said unidirectional rotational displacement of said members.

4. A control mechanism comprising: a first longitudinally extending member including a predetermined portion; a second longitudinally extending member including a circular portion having a first sector with a leading edge and a trailing edge and having a second sector, means for supporting said members for unidirectional rotational displacement relative to one another and for positioning said members so that said-circular portion of said second member defines the locus of points thereof in longitudinal alignment with said predetermined portion of said first member; means for additionally supporting said first member for bidirectional longitudinal displacement, said first member being biased toward a reference position representing a minimum longitudinal separation of said members and being adapted to control a controlled element in accordance with the displacement of said first member from said reference position; a preset cam projecting longitudinally from said first sector and comprising an inclined surface which extends from said leading edge to said trailing edge of said first sector, the slope of said surface being proportioned to displace said first member longitudinally from said reference position to a preset position corresponding to a maximum separation of said members; and a plurality of individually adjustable stop devices projecting longitudinally from and spaced along said second sector, the projection of said stop devices being in a descending progression from said trailing edge of said.

first sector so that upon relative rotation of said members said stop devices successively engage said first member to effect preselected and progressively increasing longitudinal displacements of said first member from said preset position toward said reference position; and, means for effecting said unidirectional rotational displacement of said members.

i0 longitudinally extending member including a freely rotatable cam follower supported at an end portion thereof; a rotatable second longitudinally extending member including a circular portion having a first sector with a leading edge and atrailing edge and having a second sector; means for supporting said members for unidirectional rotational displacement and for bidirectional longitudinal displacement relative to one another and for positioning said members so that said circular portion of said second member defines the locus of points thereof in longitudinal alignment with' said end portion of said first member; said members being biased toward a reference position representing a minimum longitudinal separation therebetween and being adapted to control a controlled element in accordance with the displacements of said membars from said reference position; a preset cam projecting longitudinally from said first sector and comprising an inclined surface for engaging said cam follower, said surface extending from said leading edge to said trailing edge of said first sector and having a slope proportioned to displace said first member longitudinally from said reference position to a preset position corresponding to a maximum separation of said members; and a plurality. of individually adjustable stop devices projecting longitudinally from and spaced along said second sector, the projection of said stop devices being in a descending progression from said trailing edge of said first sector so that upon relative rotation of said members said stop devices successively engage said first member to effect preselected and progressively increasing longitudinal displacements of said first member from said preset position toward said reference position; and means for effecting said unidirectional rotational displacement of said members.

6. A control mechanism comprising: a longitudinally adjustable plunger, including a freely rotatable cam follower supported at an end portion thereof, biased toward a reference position and adapted to control a controlled element in accordance with its displacement from said reference position; a longitudinally extending cylinder, including a circular portion having a first sector with a leading edge and a trailing edge and, having a second sector, rotatable in a single direction and positioned so that said circular portion thereof defines the locus of points thereof in longitudinal alignment with said end portion of said plunger; a preset cam projecting longitudinally from said first sector and comprising an inclined surface for engaging said cam follower, said surface extending from said leading edge to said trailing edge of said first sector and having a slope proportioned to displace said plunger longitudinally from said reference .position to a preset position corresponding to a maximum displacement of said plunger; and a plurality of individually adjustable stop devices-projecting longitudinally from and spaced along said second sector, the projection of said stop devices being in a descending progression from said trailing edge of said first sector so that upon relative rotation of said cylinder said stop devices successively engage said plunger to effect preselected and progressively increasing longitudinal displacements of said plunger from said preset position toward said reference position; and means for rotating said cylinder in said single direction.

7. A controlmechanlsm comprising: a first longitudinally extending member including a .predetermined portion; a second longitudinally extending member including a circular portion having a first sector with a leading edge and a trailing edge and having a second sector; means for supporting said members for unidirectional rotational displacement relative to one another and for positioning said members so that said circular portion of said second member defines the locus of points thereof .in longitudinal alignment with said predetermined portion of said first member; means for securing one of said members in an adjustably fixed position along a longitudinal axis; means for suppo ting the other of said members for bidirectional longitudinal displacement and for biasing said other member toward a reference position; said other member :being adapted to control a controlled element in accordance with its displacement from said reference position; a preset cam projecting horizontally from said first sector and comprising an inclined surface which extends from said leading edge to said trailing edge of said first sector, the slope of said surfacebeing p-roportioned to displace said other of said members longitudinally from said reference position to a preset position corresponding to a maximum sepmation of said members, and a plurality of 12 individually adjustable stop devices projecting longitudinally from and spaced along said second sector, the projection of said stop devices being in a descending progression from said trailing edge of said first sector so that upon relative rotation of said members said stop devices successively engage said first member to effect pre-.

selected and progressively increasing longitudinal displacements of said other member from said preset position toward said reference position; and means for effecting said unidirectional rotational displacement of said members.

BASIL A. BELS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'I'ENTS Number Name Date 877,687 Westiahl Jan. 28, 1908 1,684,519 Scheerbarth Sept. 18, 1929 1,965,281 Deisch July 3, 1934 2,066,246 Bolton Dec. 29, 1936 2,196,416 Jacob Apr. 9, 1940 2,219,302 Foster Oct. 29, 1940 2,316,720 Wandrey Feb. 9, 1943 2,399,702 White May 7, 1946 

